Place the butter or margarine, potatoes, onion and celery in a large pot over high heat. Add water to cover and cook for 20 minutes, or until potatoes are tender.

Puree the cooked potato mixture in small batches in a blender or food processor. Return the pureed mixture to the pot over medium heat. Add the kielbasa, ranch dip mix and half-and-half. Stir well and season with salt and pepper to taste. Allow soup to heat through, but do not boil.